The present invention relates to an electrical switch, and, more particularly, to a cam follower mechanism for a rotary switch as found in a transmission selection rotary switch of a vehicle.
Electrical switches are well known. One common type of electrical switch is a rotary switch having a rotating shaft connected to a terminal capable of making or breaking an electrical connection with one or more other terminals. Rotary switches may convert positions into binary numbers; such switches are known as coded switches. For example, a three terminal coded switch can output a binary code equivalent to eight positions. The three terminals electrically reflecting the binary equivalent of the eight switch positions.
Rotary switches contain contacts which may be non-shorting contacts, otherwise known as break-before-make contacts, which operate by breaking a preceding circuit before closing the next circuit. Converse to that, rotary switches may also have shorting contacts, which operate as make-before-break contacts. The make-before-break feature indicates that an electrical contact is made with the next position before breaking the electrical contact with the current position.
Rotary switches are also known which have three ball bearings therein to provide a rotational and a detent feature within the rotary switch. Rotary switches are known to have moveable electrical contacts therein, which slide from one electrical contact on a printed circuit board or substrate to another electrical contact on the printed circuit board or substrate. The wiping action of a movable contact relative to a stationary contact within the rotary switch allows the rotary switch to connect electrical circuits subject to the rotational position of the shaft.
A problem with rotary switches is that the wiping of the movable contact from one stationary contact to another stationary contact causes a migration of conductive material across a nonconductive separating material, thereby causing intermittent or shorted conditions among the stationary contacts.
What is needed in the art is a break-before-make rotary switch, which doesn""t short between contacts.
The present invention provides an apparatus for breaking electrical contact on both a common and signal surface before making electrical contact with a second signal surface.
The invention comprises, in one form thereof, a rotary switch including a housing and a rotor rotationally connected to the housing. The rotor is rotatable about a first axis. A cam follower is connected to the rotor, and has a cam surface substantially centered about a radial axis. The radial axis is normal to the first axis. An electrical contact has a contact surface spaced from the cam surface along the radial axis.
The invention comprises, in another form thereof, a method of passing a signal to a common terminal. The method includes steps of providing a rotary switch having a plurality of conductors and an electrical contact connected to a cam follower, the cam follower being connected to a rotor rotatable about a first axis, and biased toward at least one of the conductors with a biasing device in a direction substantially parallel to the first axis, the electrical contact being electrically connectable with at least one of the plurality of conductors; placing an electrical signal on at least one of the plurality of conductors; and connecting the electrical signal through the electrical contact to the common terminal.
The invention comprises, in yet another form thereof, a transmission gear selection switch including a housing and a rotor at least partially disposed in the housing. The rotor is rotatable about a first axis. A cam follower is connected to the rotor and is movable along a second axis, the second axis being parallel to the first axis. The cam follower is disposed to follow a path in the housing. At least one ridge is positioned along the path, oriented along a corresponding radial axis, the radial axis being normal to the first axis.
An advantage of the present invention is that the rotary switch breaks both a common and a signal contact by movement of a single cam follower.
Another advantage of the present invention is that a three contact conductor connects a common terminal to a signal terminal, the three contact connections providing mechanical stability to the conductor in the rotary switch.
Yet another advantage is that the contact is held in electrical contact with contact sectors with a spring, thereby compensating for contact wear.
Yet still another advantage is that the conductive material from one sector does not migrate to another sector since the contact is lifted from one sector and placed onto an adjacent sector.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features.